(1) Field of the Invention
The present invention relates to a compact zoom lens system, and more specifically to a zoom lens system having a short total length and suited for use with lens shutter cameras.
(2) Description of the Prior Art
As a zoom lens system having a field angle range including the standard field angle (on the order of 2.omega.=47.degree.) and a vari-focal ratio on the order of 2x, there is conventionally known a zoom lens system of the type which comprises a front lens group having negative refractive power and a rear lens group having positive refractive power, and performs variation of focal length by varying the airspace reserved between the lens groups. Since the zoom lens system of this type has the same composition as that of the retrofocus lens system, it has a merit to allow to reserve a space for arranging a mirror when said zoom lens system is used in a single-lens reflex camera. However, said zoom lens system has a long back focal length, thereby making it impossible to shorten the total length (the distance as measured from the object side surface of the first lens to the image surface), and comprises the front lens having a large diameter, thereby making it impossible to make said zoom lens system compact.
On the other hand, as a zoom lens system compact enough to be built in a lens shutter camera, there is known a zoom lens system which comprises a front lens group having positive refractve power and a rear lens group having negative refractive power. This zoom lens system is characterized in that it has the telephoto type of composition which makes it possible to shorten the total length of the zoom lens system. As the conventional examples of the zoom lens systems of this type, there are known the ones disclosed by Japanese Unexamined Patent Publication No. 201213/1982 (U.S. Pat. No. 4682860) and Japanese Unexamined Patent Publication No. 191216/1985. However, these conventional examples are designed for low vari-focal ratios on the order of 1.5 and do not correct aberrations with good balance. The zoom lens systems disclosed by Japanese Unexamined Patent Publication No. 170816/1985 and Japanese Unexamined Patent Publication No. 15115/1986 are known as the zoom lens systems of this type and having a vari-focal ratio attaining to 2, but have long total lengths. Further, these conventional examples have a defect that aberrations are not corrected sufficiently in the zoom lens systems.